Eden Rock has shore diving if you are interested in that, I was on a cruise to Cayman last week and chose a guided shore dive because I was by myself and had limited time. Eden Rock is also the name of one of the nearby reefs that we visited, the other being Devil's Grotto. Both are nice reefs with swim throughs and lots of fish, 50 feet max depth.
Eden Rock does a lot of teaching and the crowds around the tables got busy by the end of the second dive but I was told the guided tours are generally 1 or 2 people. The guides like doing tours because it's a break from their usual teaching duties.
As others said, Eden Rock is close by the tender port, I just wheeled my gear about a half mile from the tender to their shop, paid the guy inside, then suited up and went in. Not as spectacular as a wall dive but not bad if you only have a few hours and want to set your own time.
Have fun in Cayman...